Circular, V-couplings for clamping the flanges of pipes together have been used for many years, especially in pipes conducting high temperature and pressure fluids. While these couplings provide adequate clamping, they are consistently large, heavy and bulky. Thus, substantial space is required for their installation. In many situations, weight is a premium, such as in aircraft and aerospace equipment; therefore, the size of the clamp must be minimized to decrease costs. Reduction of the size and weight of the V-couplings and flanges has until now engendered a further problem of flanges being forced into non-circular deformation during tightening of the coupling. Non-circularity sometimes contributes to stiffening of the resistance to actuation of lightweight valves and other components connected to ducting by V-couplings.
There are two basic categories of pipe couplings used today. The first coupling is fabricated from sheet metal retainers attached to tension bands. They were at first in widespread use in the aircraft and aerospace industries; however, their reliability was very questionable, owing to failures of their riveted or spot welded joints and fatigue failures of their tension bands.
The second type of coupling was later introduced, using forged, cast or machined retainers, with integrally hinged ends joined by eyebolt fasteners and connecting links. While the "forged-style" couplings have proven extremely reliable and efficient, they suffer from two disadvantages, which are addressed by the present invention. First, current "forged-style" couplings use tension-type swing-bolts and links that are disposed at a considerable offset distance from the neutral axis of the coupling retainer channel section. The resultant movement produced by the fastener tightening torque causes inward rotation of the retainer ends which, in turn, locally deflects the flanges inward. Opposite the fastener, the two retainers are joined by a non-adjustable swivel link, which is offset from the circumferential loading line between the two retainers. This offset arrangement in this type of coupling is essential to the proper functioning of the coupling so that tension is transmitted through the linked retainer ends entirely symmetrically. Accordingly, the same amount of inward deflection occurring at the fastener ends of the retaining member is also produced at the hinged ends of the retaining member.
Second, current couplings employ a tension bolt, which by its nature is the component most prone to failure by fatigue and/or by overtightening. Because of the relatively long movement required for adjustment of a fastener element, any automatic safety element protecting it must have means for accommodating this long movement, such as a slotted hole. The presence of a long slot results in a large movement if the primary structure fails, before the safety element engages. This large movement results in a loosening of the coupling and separation of the flanges causing substantial leakage.
Examples of these couplings are disclosed in U.S. Pat. Nos. 1,966,039 to Muchnic; 3,575,432 to Taylor; and 3,797,836 to Halling; French Pat. No. 1,403,430 to Avica Equipment Ltd.; and British Pat. Nos. 1,126,872 to Ward et al. and 1,140,636 to Brownhill et al.